In the context of the present invention:                said vehicle can correspond to any type of vehicle that is likely to move on the ground and/or in the air; and        said obstacle, which can immaterially be a fixed element, in particular a building, or a moving object such as another vehicle for example, must be able to be avoided by said vehicle, and with a predetermined safety margin.        
More particularly, although not exclusively, the present invention applies to an aircraft, in particular a transport airplane, which is approaching an airport in order to land or is moving away after a take-off.
The avoidance maneuvers considered in the present invention are therefore phases presenting high safety risks, due in particular to the proximity of one or more obstacles. Aggravating factors can be added to the criticality of this situation, such as poor environmental conditions or reduced maneuverability of the vehicle, which make it difficult to drive and which increase the risk of collision.
Currently, on transport airplanes in particular, there are onboard collision prevention systems which ensure that a safety distance is maintained between the airplane and an obstacle. However, the avoidance trajectories proposed by these usual prevention systems are not optimal in particular when it comes to the deviation (in terms of space and time) relative to the trajectory initially followed by the airplane.
Carrying out an avoidance maneuver of excessive amplitude can in particular lead to two types of major problems, namely:                excessively increasing the time needed for the vehicle to reach its destination. This can in particular be quantified in compensation cost in the case of paying transportation of goods or passengers; and        making it necessary to apply an additional maneuver to avoid a second obstacle that did not initially present any danger. The badly performed avoidance of a first obstacle leads in this case to a new risk of collision with the second obstacle.        
Furthermore, in order to prevent emergency situations, such as, for example, a failure of a piloting for driving) system of the vehicle, a minimum safety separation with the obstacle must be ensured.
Moreover, the avoidance trajectory can be subject to external constraints such as performance limitations of the vehicle or traffic and movement rules in the environment.
The object of the present invention is to remedy the abovementioned drawbacks. It relates to a method for assisting in the driving of a vehicle in motion, in particular an aircraft and in particular a transport airplane, which is moving (on the ground or in flight) along an initial trajectory, in an environment containing at least one obstacle, fixed or moving, which must be avoided.
To this end, according to the invention, said method is noteworthy in that the following successive sequence of operations is carried out automatically and repetitively:    A/ a check is carried out, while the vehicle is moving, to see if at least one condition for modifying the trajectory because of an obstacle is fulfilled; and    B/ if such a condition is fulfilled:            a) a criterion is determined which depends on at least some of the following parameters:                    a risk of collision with the obstacle;            spatial deviation from the initial trajectory; and            time remaining before reaching a planned destination;                        b) information is determined, at least from the current position of the obstacle and from the current position of the vehicle, relating to an avoidance trajectory that makes it possible to minimize said criterion and that is such that, when it is followed by said vehicle, it enables said vehicle to avoid said obstacle while reaching the planned destination; and        c) said information for example, control instructions for control means, in particular control surfaces of an aircraft) relative to the avoidance trajectory is used to assist in the driving of the vehicle.        
Thus, thanks to the invention, an optimum avoidance trajectory is automatically determined which enables the vehicle to avoid an obstacle, while enabling it to reach a particular destination, and this optimum avoidance trajectory is used to assist in the driving of the vehicle, as specified hereinbelow. The method according to the invention thus remedies the abovementioned drawbacks, in particular by providing an avoidance trajectory that is optimal when it comes to the deviation (in terms of space and time) relative to the trajectory initially followed by the vehicle.
Furthermore, since this method is implemented at least partially automatically, the workload of the pilot or pilots is not increased.